Crankcase ventilation



Dec. 26, 1967 w. D. PITTSLEY 3,359,960

CRANKCAS E VENT ILAT ION Filed Dec. 21, 1964 I PRESSURE DIFFERENTIAL I x Arrow/5y United States Patent O 3,359,960 CRANKCASE VENTILATION William D. Pittsley, Flint, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Dec. 21, 1964, Ser. No. 419,686 7 Claims. (Cl. 123119) This invention relates to crankcase ventilation systems for internal combustion engines and, more particularly, to a crankcase ventilation valve for controlling the flow of vapors from the crankcase to the induction system of an internal combustion engine.

It is old in the art to provide an internal combustion engine with a crankcase ventilation system wherein crankcase vapors are carried from the engine crankcase to the inlet manifold or some other portion of the engine induction system. This type of system provides for the removal of blowby and other vapors which tend to collect in engine crankcases by drawing them into the induction system with the vacuum naturally formed by the operation of the engine. Such a system usually also includes provision for the addition of fresh air to the crankcase which mixes with the crankcase vapors and is carried into the induction system therewith.

Because of the wide variation in induction system vacuum over the range of engine operating conditions, the incorporation of a crankcase ventilation flow control valve is necessary to adjust the volume of flow to a desirable level for the various conditions which exist during engine operation.

Prior art construction One type of flow control valve which has been extensively used is shown in McMullen 2,716,398. This type of valve includes a generally cylindrical housing having an orifice therein and carrying a reciprocably movable plunger spring biased away from the orifice. An increase in pressure differential across the valve causes the plunger to seat on the orifice, stopping flow therethrough. However, a bypass passage is provided within the plunger through which a controlled amount of flow is permitted when the plunger is seated on the orifice.

Ventilation valves of this type have been found in service to be subject to two particular problems; one, the central orifice in the plunger is subject to plugging by deposits from the crankcase vapors which prevent the normal flow of vapors from passing through the valves under conditions of high vacuum such as at engine idle and under nearly closed throttle operating conditions; two, vibration of the plunger is sometimes quite severe to the point where Wear of the orifice and plunger seat occurs and, in addition, such vibration changes the flow curve significantly so that the valve tends to pass a larger amount of crankcase vapors than is desired under certain operating conditions. Such vibration may also affect noticeably the operation of the vehicle under certain load conditions due to changes caused in air-fuel ratios.

In an extensive investigation, ventilation control valves of this general type were found to behave in vibration essentially as undamped systems such that the natural frequency of vibration could be calculated from the relationship f 16.6 (k/ W) wherein f =natural frequency of mass spring system in cycles per second k=spring rate in ounces per inch W=Weight of the plunger plus the weight of the spring in grams. I

The variables determining the natural frequencies of certain valves made according to the McMullen construction were determined to be Spring rate= ounces per inch Spring weight=.80 gram Plunger weight=5-7 grams.

Substituting these values in the above relationship, the natural vibration frequency of these valves was found to be in the range of approximately 45-55 cycles per second. This compares with engine firing frequencies, for an idle speed of 450 rpm, of 30 cycles per second for an 8-cylinder engine and 225 cycles per second for a 6- cylinder engine. Thus, it is seen that as engine speed is increased slightly above idle, the engine firing frequencies coincides with the natural frequency of the valve.

Observations made under actual engine operating conditions revealed that whenever the engine was operated at a firing frequency near that of the natural frequency of Vibration of the valve, the valve plunger was forced into vibration sympathetic with the firing frequency. The discovery of this connection between engine firing frequency and excess vibration of the ventilation valve plunger marked a significant step toward the solution of this problem.

Improvements of present invention In order to prevent this undesirable vibration of the valve plunger, the present invention provides for reducing the natural frequency of the plunger to a figure below that of the engine firing frequency for all conditions of engine operation which may be critical to any degree, as for example light load operation at low speeds or in some cases normal idling. With this in mind, ventilation valves according to the present invention were designed to have natural frequencies in the range of from approximately 19-25 cycles per second, which is at or below engine firing frequencies even at idle conditions and well below any critical speed of operation under load for most vehicle engines. This change was accomplished by designing the valve to have the following pertinent values:

Spring rate=15 ounces per inch Spring weight=.46 gram Plunger weight=7-9 grams.

The most significant change was the reduction of the spring rate by a factor of four while the plunger weight was only slightly increased. Through this method the size of the ventilation valve was kept relatively small while accomplishing the purpose of bringing the natural frequency down into a nonsensitive range.

In order to make such a substantial reduction in spring rate and still obtain a ventilation valve construction giving a desirable curve of fluid flow versus pressure differential across the valve, it was necessary to increase the travel of the plunger over the flow range in direct proportion to the decrease in spring rate. To accomplish this, the plunger was formed with a relatively gradual taper especially in the critical flow control areas. For this reason, slight vibration of the valve, if it does occur, does not change the flow characteristics as much as occurred with the prior design and this further increases the stability of operation of the valve.

One additional observation from tests of the McMullen construction was that when the valve plunger was forced into vibration, it would intermittently strike against the valve seat and then bounce away from it. This resulted in increasing the average flow through the valve during vibration since the valve was opened excessively wide when away from the valve seat but was limited to a fixed closed position upon striking the valve seat. Thus, in the valve of the present invention, a non-closing construction was utilized in which the minimum flow area is provided by a cylindrical portion of the plunger adjacent the head thereof. This makes additional plunger travel available before the head strikes against the stop member during which there is no change in the restrictive effect of the valve on the flow of fluids therethrough. For this reason, even if some slight vibration does occur, there will be little or no change in the flow rate due to this vibration since, in the control zone, the valve is free to move both sides of its ideal location resulting in an averaging of the flows over the range of vibration. Of course, if severe vibration were to be permitted, a consequent upsetting of the flow would undoubtedly occur.

Use of the non-closing construction for the valve also permitted the elimination of the bypass orifice. In the present construction, the plunger controls the flow by movement into and out of the outlet passage, the edge of which comprises a flow restricting orifice. The plunger is permitted to contact the orifice in this movement which helps to keep the plunger free of deposits. In addition, a part of the plunger adjacent the head acts as a dirt storage area and retains, out of the fiow stream, some of the deposits which are scraped from the plunger flow control surface. These features all combine to assure a valve construction which is almost completely free of problems caused by internal deposits.

Features of the invention It is, therefore, a feature of this invention that it provides an engine crankcase ventilation system including a crankcase ventilation valve having a reciprocating flow control plunger biased by resilient means, the combination having a natural frequency of vibration less than the firing frequency of the engine at critical operating speeds to prevent the plunger from being forced into severe vibration.

A further feature of the invention is that the travel of the plunger is increased over prior art devices so that limited vibration of the plunger will have less effect on the flow curve as compared to prior art devices.

Another feature of the invention is that provision is made for over-travel of the plunger beyond the position of minimum orifice size such that the plunger is normally free to vibrate slightly in both directions from its control position thereby resulting in a minimum disturbance of the flow curve due to vibration of the plunger.

Still another feature of the invention is that the movement of the plunger within the control orifice provides a self-cleaning action, removing deposits which tend to form on the plunger and resisting changes in the flow curve which would come from plugging of the orifice.

A still further feature of the invention is that a portion of the plunger body is prevented from entering the orifice, such portion being located out of the flow stream so as to provide a dirt trapping surface which is adapted to retain a substantial volume of the deposits which are scraped toward the dirt carrying surface by the working of the plunger in the orifice.

These and other features of the invention will be more apparent from the following description and drawings which disclose one embodiment of an engine having a crankcase ventilation system and a crankcase ventilation valve according to the invention and wherein:

FIGURE 1 is a front elevational view of an engine having a crankcase ventilation system including a flow control valve according to the invention;

FIGURE 2 is a cross-sectional view of the flow control valve of FIGURE 1 showing the plunger in the position of least flow restriction;

FIGURE 3 is a cross-sectional view of the valve of FIGURE 2 but with the plunger in the position of greatest restriction to flow from the crankcase to the induction system;

. 4 FIGURE 4 is a cross-sectional view of the valve of FIGURE 2 taken along the line '4-4; and

FIGURE 5 is a graphic presentation of a desired flow curve.

General description Referring now to the drawings, FIGURE 1 illustrates an internal combustion engine generally indicated by numeral 10 having a plurality of cylinders 12 arranged in a pair of banks angularly displaced with respect to one another. Cylinders 12 include pistons 20 arranged for reciprocation therein and connected by connecting rods 22 with the respective throws of crankshaft 24. The throws of the crankshaft are arranged in the usual manner to reciprocate pistons 20 successively between upper and lower positions in a predetermined sequence.

The engine includes conventional cylinder heads 26 closing the tops of the cylinders and forming, in cooperation with the pistons, combustion chambers 28. An induction system is provided for introducing a combustible mixture into the combustion chambers and includes inlet ports 30 formed in the cylinder heads, an inlet manifold 32 connecting with the inlet ports, a carburetor 34 mounted on the inlet manifold and an inlet air cleaner 36 carried by the carburetor.

In the cycle of engine operation a combustible mixture is inducted into each cylinder and is ignited when the piston is near the upper end of its stroke, burning the mixture and causing the crankshaft to rotate. The rate at which the cobustible mixture in the various cylinders is ignited in sequence is known as the firing frequency of the engine.

/ Engine 10 further includes a crankcase ventilation system including a conduit 38 extending between the inlet manifold 32 and one of the engine rocker covers 40, the interior of which communicates through internal passages, not shown, with the crankcase 12. A crankcase ventilation flow control valve 42 is mounted on the rocker cover and connects with one end of the conduit 38 thereby providing a flow path for crankcase vapors through valve 42 and conduit 38 into inlet manifold 32 in which they are mixed with the combustible mixture to be introduced into the cylinders.

On the other rocker cover 44, a conventional breather cap 46 is located for the purpose of permitting the induction of fresh air through the rocker compartment and into the crankcase, as is commonly done, to assist in removal of the crankcase vapors.

In FIGURE 2 is shown the construction of the crankcase ventilation flow control valve 42 of FIGURE 1. The valve is shown to include a housing 48 having a cylindrical internal wall portion 50 partially defining a generally cylindrical cavity 52 in which is disposed a plunger 54. At one end of cavity 52 is formed an annular seat 56 which is adjacent an inlet connecting portion 58. This portion is adapted for connection with a resilient coupling and includes a central passage 60 extending from cavity 52 and coaxial therewith. At the other end of the cavity, the housing is crimped over and retains an insert portion 62 which includes an outlet connecting portion 64 having a central passage 66 connecting with cavity 52 and also coaxial therewith. Adjacent the inner end of passage 66, an annular spring seat 68 is provided from which projects a cylindrical extension 70, terminating in an annular stop portion 72.

Plunger 54 comprises an elongated body portion 74 having an axis lying generally along the axis of the housing and is provided at the inlet end with a radially extending head 76 adapted to bear against the cylindrical wall 50 of cavity 52. As shown in FIGURE 4, the head 76 is provided with cutout areas 78 around its periphery to permit unrestricted flow of crankcase vapors past the head.

A coil spring 82 extends between plunger 54 and annular seat 68 engaging the plunger at the junction of body portion 74 and head 76 and biasing the plunger in the direction of annular seat 56. The spring is formed in a generally cylindrical shape except for the last coil 84 which is formedof smaller diameter to pilot on the end of body portion 74 thereby maintaining the spring generally concentric with the axis of the housing and holding the working coils in non-rubbing relationship with both the housing wall 52 and the plunger body portion 74.

The plunger is adapted to be moved into the passage 66 and to coact with the edge 90 thereof, which acts as an orifice, to form a restriction of variable area for controlling the flow of crankcase vapors through the valve. To this end, the plunger is formed with its maximum diameter adjacent the head portion 76 and sufficiently small to allow the plunger to enter into passage 66. The cross-sectional area of the body generally decreases as the distance away from the head 76 is increased until at the opposite end the smallest diameter occurs.

The particular shape of the plunger may be varied as necessary to obtain the desired rate of fluid flow at each position of the plunger. However, in the preferred embodiment of FIGURES 2 and 3, the plunger has a cylindrical portion adjacent head 76, adjacent to which are three tapered portions increasing in the amount of taper in the order of their distance away from head 76. At the extreme end of the body is a second cylindrical portion of relatively small diameter which projects through annular edge 90 at all times to prevent the plunger from vibrating out of alignment therewith.

Operation In operation, the position of plunger 54 varies with the difference in pressure between the engine crankcase and the induction system which are connected to ends 58 and 64 of the housing respectively. At wide open against the bias of the spring away from seat 56 and further into passage 66 reducing the cross-sectional area of the restriction at edge 90 so that a comparable increase in flow of crankcase vapors through the valve is prevented and the rate of flow is controlled in a desired predetermined manner. Should pressure differential increase sufiiciently, as might occur under closed throttle conditions when a vehicle is coasting and induction system vacuum becomes unusually high,-the head 76 of the plunger will be drawn against stop portion 72, as shown in FIG- URE 3. This limits the compression of spring 82 so as to permit free fiow of vapors between the coils as well as through the cutout areas 78 between portion 96 and the spring coils, thereby permitting flow to pass through the limited controlling restriction at edge 90 at all times. During its controlling movement, as above described,

the head end of the plunger is held relatively centered by the guiding action of the head riding against cylindrical wall 50 of the plunger body; however, the other end of the plunger is unsupported and is thereby free to slide against the edge 90 of passage 66. This action tends to scrape from the plunger body deposits which tend to form thereon due to the passage of crankcase vapors through the valve. Some of these deposits are, of course, broken free and carried with the vapors into the engine induction system while others tend to cling to the plunger and are pushed toward the head 76 collecting upon a portion 96 of the plunger body which is prevented from entering passage 66 by the engagement of the head with stop 72., This portion of the plunger body represents a deposit storage area 96 which collects some of the deposits which might otherwise build up around the housing orifice or at other points so as to partially block the flow of crankcase vapors through the valve. Deposits collected on portion 96 are retained out of the normal flow path of the crankcase vapors so that flow through the valve is substantially unalfected by such deposits.

FIGURE 5 illustrates a typical graph of pressure differential versus flow rate for a crankcase ventilation valve according to the present invention. When the pressure dilferential is low, the valve plunger remains at or near the wide open position shown in FIGURE 2. Flow through the valve increases as the pressure diflerential increases up to a desired maximum flow at the control point, where further increase of the pressure differential begins to move the valve plunger into passage 66 increasing the restriction to flow past edge 90. Further increase of the pressure differential results, due to the predetermined plunger shape, in a controlled decrease in crankcase ventilation flow to a minimum flow rate which is permitted at maximum pressure differential conditions.

The investigations, previously mentioned, showed that ventilation valves of this general construction were inherently stable in the portion of their flow range in which the flow increased with increasing pressure differential. However, during the major portion of the flow curve, the flow decreases with increasing pressure dilferential and an unstable condition results in which any dislocation of the plunger position is magnified to produce a condition of vibration. For instance, if the plunger is jarred toward a more restrictive position than is called for, flow is reduced resulting in a momentary increase in pressure on the upstream side and a decrease on the downstream side which tends to further dislocate the plunger from its desired position. This dislocation builds up excessive force in the spring, returning the plunger to its normal position; but the inertia involved carries the plunger past this position resulting in an excessive flow and further overtravel of the plunger in this direction and so on. For this reason, the increased travel required to upset the flow and the reduced spring rate of valves, according to the present invention, aid substantially in the stability of the system.

Although the herein described valve construction has been found to be very satisfactory in the applications to which it has been applied, it should be obvious that, if desired, the natural frequency could be further reduced by increasing plunger weight or, alternatively, reducing spring rate. Changes in the spring rate would, of course, require equivalent changes in the configuration and allowable travel of the plunger in order to obtain the same flow curve for a given set of conditions.

Additional modifications within the scope of the present invention will be apparent to those skilled in the art and the invention is, therefore, to be limited only by the language of the following claims.

What is claimed is:

1. A crankcase ventilation valve for use in an internal combustion engine having an induction system and a crankcase, said crankcase ventilation valve being adapted for connection between the crankcase and the induction system to control fluid flow therebetween and comprising a housing having an orifice therein to restrict fluid flow therethrough,

a valve element in said housing and having a generally tapered body portion and a head at one end thereof, said head extending radially outboard of said body portion into close proximity with said housing to center said body portion end in said housing, said tapered body portion being of smaller diameter throughout its length than said orifice and movable thereinto in response to an increase in pressure differential between the crankcase and the induction system so as to increase the restriction to fluid flow through said orifice,

coil spring means between said head and said housing and biasing said valve element away from the orifice and in the direction of decreased restriction, said spring means having at least one coil adjacent said head and fitted closely around said body portion and a plurality of additional coils being of substantially equal diameter and arranged to clear both said body portion and the housing walls whereby said spring, said body portion and said head cooperate to maintain said spring coils in nonrubbing relationship with said housing and said body portion thereby reducing wear of said spring coils and stop means in said housing and adapted to be engaged by said valve element head, said stop means preventing the closing of said spring coils below a predetermined clearance to permit the free passage of crankcase vapors therebetween at all times and to prevent part of said body portion from entering said orifice whereby a limited volume of deposits is enabled to collect upon said body portion part within the clearance between said part and said spring coils without substantially blocking fluid fiow through the orifice. 2. In combination, an internal combustion engine having a crankcase, an induction system and a plurality of cylinders and normally operable under load above a predetermined cylinder firing frequency and a crankcase ventilation valve connected with said crankcase and said induction system and including a spring biased plunger reciprocably movable to control the flow of crankcase vapors therethrough, said plunger and spring having a natural frequency of vibration below said predetermined cylinder firing frequency.

3. In combination, an internal combustion engine having a crankcase and an induction system and normally operable under load at a cylinder firing frequency of not less than 25 cycles per second and a crankcase ventilation valve connected between the crankcase and the induction system and including a spring biased plunger reciprocably movable to control the flow of crankcase vapors therethrough, said plunger and spring having a natural frequency of vibration below approximately 25 cycles per second.

4. In combination, a crankcase ventilation valve and an internal combustion engine normally operable under load above a predetermined cylinder firing frequency and having a plurality of cylinders, an induction system connecting with the cylinders and a crankcase, said crankcase ventilation valve being connected between the crankcase and the induction system to control fluid flow therebetween and comprising a housing having an orifice therein to restrict fluid flow therethrough,

a valve element in said housing having a generally tapered body portion and movable in said orifice in response to an increase in pressure differential between the crankcase and the induction system so as to increase the restriction to fluid flow through the orifice,

spring means having a predetermined rate and biasing the valve element away from the orifice and away from the direction of increased restriction,

said valve element and said spring means comprising a mass-spring system having a predetermined inertia,

the inertia of the system and the rate of the spring means being such that the natural frequency of the system is less than said predetermined cylinder firing frequency whereby forced vibration of the valve element due to engine firing is substantially prevented.

5. In combination, a crankcase ventilation valve and an internal combustion engine normally operable at or above a prescribed idle firing frequency and having a plurality of cylinders, an induction system connecting with the cylinders and a crankcase, said crankcase ventilation valve being conducted between the crankcase and the induction system to control fluid flow therebetween and comprising valve means movable in response to an increase in pressure differential between the crankcase and the induction system so as to increasingly restrict fluid flow and resilient means having a predetermined rate and biasing the valve means away from the direction of increased restriction,

said valve means and said resilient means comprising a mass-spring system having a predetermined inertia,

the inertia of the system and the rate of the resilient means being such that the natural frequency of the system is not substantially greater than the normal engine idle firing frequency whereby forced vibration of the valve means due to engine firing during above idle engine operating speeds is substantially prevented.

6. The combination of claim 5 wherein the inertia of the mass-spring system and the rate of the resilient means are such that the natural frequency of the system is less than the normal idle firing frequency whereby forced vibration of the valve means due to engine firing is substantially prevented.

'7. In combination with an internal combustion engine having an induction system and a crankcase, a crankcase ventilation valve connected between the crankcase and the induction system to control fluid flow therebetween and comprising a housing having an orifice therein to restrict fluid flow therethrough,

a valve element in said housing and having a generally tapered body portion and a head at one end thereof, said head extending radially outboard of said body portion into close proximity with said housing to center said body portion end in said housing, said tapered body portion being of smaller diameter throughout its length than said orifice and movable thereinto in response to an increase in pressure differential between the crankcase and the induction system so as to increase the restriction to fluid flow through said orifice,

coil spring means between said head and said housing and biasing said valve element away from the orifice and in the direction of decreased restriction, said spring means having at least one coil adjacent said head and fitted closely around said body portion and a plurality of additional coils being of substantially equal diameter and arranged to clear both said body portion and the housing walls whereby said spring, said body portion and said head cooperate to maintain said spring coils in nonrubbing relationship with said housing and said body portion thereby reducing wear of said spring coils,

stop means in said housing and adapted to be engaged by said valve element head, said stop means preventing the closing of said spring coils below a predetermined clearance to permit the free passage of crankcase vapors therebetween at all times and to prevent part of said body portion from entering said orifice whereby a limited volume of deposits is enabled to collect upon said body portion part within the clearance between said part and said spring coils without substantially blocking fluid flow through the orifice, and

said internal combustion engine being normally operable under load above a predetermined cylinder firing frequency, said coil spring means having a predetermined rate and said valve element and said spring means comprising a mass-spring system having a predetermined inertia, the inertia of the system and the rate of the spring means being such that the natural frequency of the system is less than said predctfigrrnincd cylinder firing frequency whereby forced 10 vibration of the valve element due to engine firing 2,620,125 12/1952 Kilchenmann 230-232 X under load is substantially prevented. 3,105,471 10/ 1963 Macpherson et a1. 123-119 References Cited 3,105,477 10/1963 Lowther 123119 3,198,208 8/1965 Tramontini 123119 X UNITED STATES PATENTS 5 3,263,699 8/1966 Givler et a1. 137-480 1,696,797 12/1928 Fornaca 123-90 2,35 9,485 10/1944- Lowther 123--119 AL LAWRENCE SMITH, Primary Examiner. 

1. IN COMBINATION, AN INTERNAL COMBUSTION ENGINE HAVING A CRANKCASE, AN INDUCTION SYSTEM AND A PLURALITY OF CYLINDERS AND NORMALLY OPERABLE UNDER LOAD ABOVE A PREDETERMINED CYLINDER FIRING FREQUENCY AND CRANKCASE VENTILATION VALVE CONNECTED WITH SAID CRANKCASE AND SAID INDUCTION SYSTEM AND INCLUDING A SPRING BIASED PLUNGER RECIPROCABLY MOVABLE TO CONTROL THE FLOW OF CRANKCASE VAPORS THERETHROUGH, SAID PLUNGER AND SPRING HAVING A NATURAL FREQUENCY OF VIBRATION BELOW SAID PREDETERMINED CYLINDER FIRING FREQUENCY. 